Merge pull request #4026 from dotCooCoo/fix/control-app-nap

Control: requests are answered at full speed while the window is hidden on macOS

apps/vectorcraft/Cargo.toml

@@ -62,8 +62,8 @@ windows = { version = "0.62", features = ["Win32_Graphics_DirectWrite", "Win32_U
 muda = { version = "=0.21.1", default-features = false }
 objc2 = "0.6"
 objc2-app-kit = { version = "0.3", default-features = false, features = ["std", "block2", "objc2-core-foundation", "NSApplication", "NSButton", "NSColor", "NSColorSampler", "NSColorSpace", "NSControl", "NSMenu", "NSEvent", "NSPasteboard", "NSPopUpButton", "NSResponder", "NSSavePanel", "NSTextField", "NSTextInputContext", "NSView", "NSWindow"] }
-# Files opened from Finder and the Dock (src/open_documents.rs) and pasted bitmaps (src/clipboard.rs); both already come with winit, muda and rfd.
-objc2-foundation = { version = "0.3", default-features = false, features = ["std", "block2", "NSArray", "NSData", "NSGeometry", "NSNotification", "NSOperation", "NSString", "NSURL"] }
+# Files opened from Finder and the Dock (src/open_documents.rs), pasted bitmaps (src/clipboard.rs) and the control channel's App Nap activity (src/control_server.rs); both already come with winit, muda and rfd.
+objc2-foundation = { version = "0.3", default-features = false, features = ["std", "block2", "NSArray", "NSData", "NSGeometry", "NSNotification", "NSOperation", "NSProcessInfo", "NSString", "NSURL"] }
 block2 = "0.6"
 # The window's AppKit view, to centre its buttons on the app bar (src/mac_window.rs). MIT OR
 # Apache-2.0 OR Zlib, already in the build through eframe and winit.

apps/vectorcraft/src/control_server.rs

@@ -67,10 +67,31 @@ pub fn start(port: u16, ctx: egui::Context) -> Receiver<ControlRequest> {
         }
     };
     eprintln!("vectorcraft: control server listening on 127.0.0.1:{port}");
+    #[cfg(target_os = "macos")]
+    keep_answering();
     std::thread::spawn(move || accept_loop(listener, tx, ctx));
     rx
 }
 
+/// The activity the control channel holds on macOS: work the user asked for, which may let the
+/// system sleep when idle, with full timer precision. Without it, App Nap lowers every thread to
+/// the lowest priority within about a minute of the window no longer being visible.
+#[cfg(target_os = "macos")]
+fn activity_options() -> objc2_foundation::NSActivityOptions {
+    use objc2_foundation::NSActivityOptions;
+    NSActivityOptions::UserInitiatedAllowingIdleSystemSleep | NSActivityOptions::LatencyCritical
+}
+
+/// Begins the control channel's activity. It lasts until the process ends.
+#[cfg(target_os = "macos")]
+fn keep_answering() {
+    use objc2_foundation::{NSProcessInfo, NSString};
+    let reason = NSString::from_str("Answering control requests");
+    let activity = NSProcessInfo::processInfo().beginActivityWithOptions_reason(activity_options(), &reason);
+    // The token is never released or passed to `endActivity`, so the activity lasts for the process's lifetime.
+    std::mem::forget(activity);
+}
+
 fn accept_loop(listener: TcpListener, tx: Sender<ControlRequest>, ctx: egui::Context) {
     let open = Arc::new(AtomicUsize::new(0));
     for stream in listener.incoming().flatten() {
@@ -642,4 +663,17 @@ mod tests {
         assert!(line.contains("too many control connections"), "{line}");
         drop(held);
     }
+
+    // A test process is not an app that App Nap applies to, so this checks the activity the
+    // channel asks for; the throttling itself shows only in a running app with its window hidden.
+    #[cfg(target_os = "macos")]
+    #[test]
+    fn the_control_channel_keeps_the_app_at_full_priority_on_macos() {
+        use objc2_foundation::NSActivityOptions;
+        let options = activity_options();
+        assert!(options.contains(NSActivityOptions::LatencyCritical), "without it App Nap still lowers the priority to 20");
+        assert!(options.contains(NSActivityOptions::UserInitiatedAllowingIdleSystemSleep));
+        assert!(!options.contains(NSActivityOptions::IdleSystemSleepDisabled), "the channel must not keep the Mac awake");
+        keep_answering();
+    }
 }

docs/control-protocol.md

@@ -51,7 +51,8 @@ A request the app hasn't answered after **60 s** gets `{"ok": false, "error": "t
 app had not started it (it was busy, or its window wasn't being drawn), the request is withdrawn
 and never runs, and the error says "will not run": retrying is safe. If the app was already
 running it, the error says "still running": it may yet complete, so check the document before
-retrying.
+retrying. On macOS the app keeps itself out of App Nap while the control channel is on, so it keeps
+answering with its window hidden, minimized or covered, or with the screen locked.
 
 ## Confining file access